Li Ion compared to FLA? Sorry. Not even close. Maybe in some market areas but I can get a VERY robust and durable 220ah 6v golf cart battery for $85. Mine are now over 4 years old and still have actually a bit better than rated capacity. They have been routinely used to 50% SOC and occasionally down to less than 40%. And no BMS or backup BMS needed. One 200a fuse. That's it. Recovered LiIon modules? On a boat? well, okay. As long as your system has some voltage flexibility so if you have to isolate a failed or failing parallel block from the series, you can still charge and operate. I have thought about trying to find electric car modules... the Tesla packs seem to be very nice, but everyone selling seems to think that they are made of gold. And a BMS failure could be well, sort of bad. So as far a Lithium types go, I think it is for me a question of LiFePO4 prismatics or non lithium.
I did once run my boat for almost 6 miles on a 48v 20ah Li Ion ebike battery. That was interesting. I think in a dinghy type situation a portable LiIon pack would be great.
No argument from me, on prop inefficiency. Props are power hungry lazy beasts. At low speeds there are options for optimizing, though. At 2 or 3kts a well designed paddlewheel would work well I think. Got to be slow enough that the paddles are not wasting energy by lifting or throwing water out of the water. At anything much less than 10kts a Kort nozzle increases efficiency, though at 10kts or more the extra drag makes it become less efficient. And of course if you can go deep enough with the shaft, a very large high aspect moderate pitch two blade prop would be wonderful, probably 30% (just a guess so don't bust my chops on this) increase in efficiency over the normal 3 or 4 blade prop, though of course it wouldn't fare well in a grounding or an encounter with a log or sunken piling.
---In electricboats@yahoogroups.com, <gcode.fi@...> wrote :
Excellent post.
Sort of agree on many of your points.
Sort of disagree on some.
If we tie a rope to a tree on shore and pull the boat - vs using the
propellers, we get 4-5x better performance in power/pull/cost.
So propellers are about 20% efficient at best - in general.
The best recovered lion battery modules cost about the same as fla/agm
per usable capacity.
Efficiency is easily seen.
I can push/pull a 70 metric tons 24 m steel powerboat at around 0.5 knots.
My power == 100 W (more like 40W).
Any prop system will consume many multiple of 100W to deliver 0.6 knots.
On 30/08/2018 16:13, king_of_neworleans wrote:
> Stick around and read the threads going back over the years. Do your
> homework. It will take you at least a year or two to reach the point
> where you can DIY your electric propulsion setup with a reasonable
> chance of success.
--
-hanermo (cnc designs)
